1. Field of the Invention
This invention relates generally to turntables, and in particular to a turntable for use in a conventional oven for supporting and rotating containers in which food stuffs are placed for baking or cooking.
2. Description of the Prior Art
The advantages associated with rotating food stuffs as they bake or cook has been known in the art for a long time as indicated in U.S. Pat. No. 557,344 issued to Shaw. The Shaw patent dates back to 1896 and describes a turntable device having a spring motor for rotating the table. Because most ovens at that time were wood or coal fired the heat was not evenly distributed within the oven chamber. Rotating the food stuffs more uniformly exposed them to the infra-red energy thereby resulting in the food stuffs being more evenly cooked or baked than if they were not rotated.
The advent of natural gas and electric ranges provided interior heating elements arranged so that a relatively uniform distribution of heat throughout the oven chamber was achieved. However, due to the various designs and manufacturers of modern ranges it was discovered that the heat was not as evenly distributed as was necessary to achieve the optimum baking and cooking results. Thus, there remains a need with conventional ovens for rotating food stuffs to obtain relatively even baking and cooking results.
The advent of microwave ovens gave rise to numerous patents being granted on devices for rotating food stuffs while cooking in a microwave. The necessity of such rotatable devices is due to "hot spots" created during cooking. It was discovered that rotating the food stuffs would more evenly distribute the infra-red energy thereby cooking the food stuffs more evenly. A common design feature of all of these rotatable devices is that they are made almost entirely of plastic to prevent arcing between the device and the interior walls of the microwave oven.
The basic design of these devices includes a turntable top mounted on a stationary base. The turntable top is usually driven by a mechanical means such as that disclosed in U.S. Pat. No. 4,523,070, issued to Jorgensen et al. The turntable top of Jorgensen is supported above the stationary base at its center by a mechanical means and at its periphery by an arrangement of ball bearings. The ball bearing configuration creates a relatively large amount of surface contact between the ball bearings and the rotatable platform thereby inhibiting ease of rotation. The additional weight of food stuffs placed on the rotatable platform slightly increases the coefficient of friction between the ball bearings and the platform so that the mechanical means driving the rotatable platform must work harder. The friction created by the ball bearings may shorten the life expectancy of the oven turntable, or lead to repair or replacement of the mechanical components, relative to a design that minimizes the surface contact between the rotatable platform and the means for supporting it above the base. U.S. Pat. Nos. 4,625,087 and 4,523,070, issued to Jorgensen et al., both disclose ball bearing methods for supporting the rotatable platform above the base, as does U.S. Pat. No. 4,746,781, issued to Dalquist, III et al.
Another oven turntable is disclosed in U.S. Pat. No. 4,808,781, issued to Liu. The turntable of Liu utilizes three flat-surfaced wheels mounted on axles to support the turntable top above the base. Again, the flat surface contact between the wheel and the turntable top creates friction that impedes the rotation of the top, especially when it is rotating relatively heavy containers.
The majority of oven turntables used for rotating food stuffs within a microwave oven are circular so they can snugly fit into the confines of the microwave. One disadvantage of this shape is that it is difficult to firmly grasp the edge of the turntable and remove it from an oven. The perimeter of a circular base does not provide enough linear edge space to adequately grasp the turntable and maintain its balance when taking it out of or placing it into the oven.
It is a desirable feature of any oven turntable to include a means for stopping its rotation when desired. U.S. Pat. No. 4,746,781, issued to Dalquist, III et al., describes such a mechanism. The locking member of Dalquist is pivotally mounted and thus prone to possible breakage because of the lateral forces exerted on the locking member when it engages a notch on the turntable wall. Also, that portion of the locking member used to activate it is located substantially underneath the turntable or base in a relatively inaccessible position that prevents ease of operation.
U.S. Pat. No. 4,808,781, issued to Liu, describes a similar device for halting the rotation of a turntable top. The Liu device is pivotally mounted and susceptible to wear and tear and possible shearing of the mounting pin resulting from lateral forces exerted thereon when it is lockingly engaged. Also, the positioning of the break arm inhibits ease of manipulation by the user.
The aforementioned patents all relate to oven turntables that are used with microwave ovens, and have their primary components made of plastics that are not capable of being used in a conventional oven.
Other concerns associated with oven turntables used in conventional ovens are: 1) keeping the production costs down; 2) maintaining a simple design for easy use and repair; 3) taking up minimal space in the oven; 4) having the oven turntable last as long as possible; and 5) using suitable materials to withstand the high temperatures.